This paper overviews novel magnetic-field-shifting techniques for enhancing the torque in a new class of asymmetric rotor pole interior permanent magnet (AIPM) machines. The principle for torque enhancement is introduced firstly. AIPM topologies are then categorized in terms of asymmetries and symmetricities of PM configuration and rotor core geometry. Subsequently, the merits and demerits of various AIPM rotor topologies in each category are analyzed and compared. Finally, torque capabilities of selected AIPM machines are compared.

A novel asymmetric interior permanent magnet (AIPM) machine is proposed in this paper for electric vehicle application. It has a skewed V-shape permanent magnet (PM) cavity, two PMs with different dimensions and an additional flux barrier outside the V-shape cavity in each pole. This asymmetric rotor topology can inherently utilize the magnetic-field-shifting (MFS) effect to reduce the current angle difference between the maximum PM and reluctance torque components, thereby enhancing the maximum synthetic torque with the same PM usage. The influences of cavity positions in the proposed AIPM and an existing AIPM with extra flux barrier inside the V-shape cavity are compared, which indicates that the proposed structure with outside flux barrier has higher average torque. Both AIPM topologies are designed with the same stator, rotor diameter, and PM usage as the conventional V-shape IPM benchmark for Prius 2010. Electromagnetic, mechanical and steady-state thermal performance of three machines are compared. The results confirm that the proposed AIPM machine can achieve significant torque enhancement due to utilizing MFS effect, compared with the existing AIPM and the IPM benchmark. Finally, a small prototype of the proposed AIPM machine is designed, manufactured and tested to validate the FE analysis.

This paper proposes a novel spoke-type asymmetric interior permanent magnet (AIPM) rotor topology that employs an additional asymmetric flux barrier in each pole of IPM synchronous machines for torque density enhancement and torque pulsating suppression without introducing any extra cost. The proposed AIPM-I machine, an existing spoke-type AIPM-II machine with asymmetric rotor profile and a conventional spoke-type IPM machine are designed and optimized with the same 12-slot/8-pole stator with non-overlapping windings as well as the same rotor diameter and PM dimensions. The effect of asymmetric flux barrier dimensions on the proposed AIMP-I machine is investigated with particular emphasis on torque characteristics. The electromagnetic performance and rotor mechanical strength of final optimal designs of three machines are compared. It confirms that the proposed AIPM-I machine can achieve significant torque enhancement and torque ripple reduction across the wide current range while also shows significantly smaller cogging torque at open-circuit condition, compared with both existing AIPM-II and conventional IPM machines. Finally, a prototype of the proposed AIPM-I machine has been manufactured and measured for validation.

This paper proposes a novel asymmetric interior permanent magnet (AIPM) rotor topology that has a mixed V-shape and spoke-type PM configuration, designated as a 1.5-layer PM structure, and asymmetric arrangement of V-shape PMs and asymmetric flux barriers. The AIPM rotor topology is employed for IPM synchronous machines to utilize the magnetic-field-shifting (MFS) effect for increasing average torque by reducing the current angle difference between peak PM and reluctance torque components. Three machines, i.e. the proposed 1.5-layer AIPM, a symmetrical 1.5-layer IPM-I and a conventional V-shape benchmark IPM-II are designed and optimized using the same stator, rotor diameter and total PM usage by global parametric optimization considering the mechanical stress. The effect of asymmetric features of the 1.5-layer AIPM rotor design, i.e. asymmetry of V-shape cavity as well as position and dimensions of flux barrier, on maximum torque and open-circuit air-gap field are investigated. The electromagnetic performances of three machines are compared. It confirms that the proposed AIPM machine has the highest maximum torque and the smallest cogging torque simultaneously. It is also revealed that the torque enhancement is achieved by both the 1.5-layer structure and MFS effect. Finally, a prototype of AIPM machine is manufactured and tested to validate the analyses.

This article proposes an efficient surrogate-assisted design optimization method based on a multicriteria optimal Latin hypercube design (LHD) for multi-objective optimization of a surface-mounted permanent-magnet vernier machine (SPMVM). An improved iterated local search (ILS) method is proposed to optimize the spatial distribution uniformity and orthogonality of LHDs so that the data feature over the wide ranges of optimization variables can be captured more efficiently. Using the optimal LHD, a highly generalizable surrogate model can be trained with fewer samples, thus greatly reducing the required number of finite element analysis (FEA) cases and improving the optimization efficiency. A prototype corresponding to the optimal design is built and measured to validate the proposed method.

This paper proposes a novel asymmetric interior permanent magnet (AIPM) rotor topology for torque enhancement and torque ripple reduction in IPM synchronous machines. The AIPM rotor structure is featured by a hybrid-layer permanent magnet configuration, i.e. for each pole one, a part of PM configuration has one-layer while the other part has two layers. It allows the magnetic-field-shifting (MFS) effect to be utilized by reducing the current angle difference between maximum PM and reluctance torque components, thereby effectively increasing the maximum resultant torque. The proposed AIPM machine and a conventional V-shape IPM machine are designed and globally parametric optimized with the same 24-slot/4-pole stator, rotor diameter and PM usage. The influence of key rotor geometric parameters of the AIPM machine on torque and open-circuit air-gap magnetic field characteristics are investigated. The comparison of electromagnetic performance confirms that significant torque enhancement and torque ripple reduction in the AIPM machine compared with the conventional V-shape IPM machine and reveals the MFS effect is essential for torque increase. Finally, an AIPM machine is manufactured and tested for validation.